new Promise(resolve => {
  setTimeout(() => {
    resolve('hello ')
  }, 10)
})
  .then(res => {
    return new Promise(resolve => {
      setTimeout(() => {
        resolve(res + 'lagou ')
      }, 10)
    })
  })
  .then(res => {
    return new Promise(resolve => {
      setTimeout(() => {
        resolve(res + 'I Love U')
      }, 10)
    })
  })
  .then(res => {
    console.log(res)
  })
